The invention relates to a contactless system for measuring centricity and diameter, said system comprising i) an optical measuring device for determining the external diameter and position of a harness in an optical measuring plane, arranged perpendicular and transverse to the central axis Z of a measuring device, wherein the harness comprises a conductor and a jacket for insulating said conductor and is pulled in the direction of the central axis Z through the measuring device; ii) an inductive measuring coil arrangement for determining the position of the conductor in an inductive measuring plane, which is also arranged perpendicular and transverse to the central axis Z of the measuring device; and iii) means which correlate the position of the harness determined with the optical measuring device and the position of the conductor determined with the inductive measuring coil arrangement and which calculate from this correlation the centricity of the conductor inside the jacket. The invention also relates to a corresponding method.
The harness in particular is a cable. When producing such harnesses and in particular cables, the jacket or coating is normally affixed to the conductor by means of extrusion, wherein the jacket can consist of one layer or can be composed of several layers that concentrically surround the conductor.
In the following, the invention is explained for reasons of simplicity with the aid of cables and the production of cables, wherein the term “cable” is representative for all types of harnesses having an electrically conductive core or carrier. It is critical that cables on the one hand have the required diameter, so that they exhibit the required electrical characteristics and, in particular, are sufficiently insulating. On the other hand, it is important that the conductor extends through the center of the cable jacket or the coating, which is particularly important for data cables and antenna cables.
Numerous devices for determining either the external diameter of a cable or the centricity of the conductor inside a cable are known. For example, reference DE 25 17 709 describes a device for measuring and controlling the wall thickness of insulated harnesses, wherein this device measures the eccentricity with the aid of an induction measurement. For this, inductive sensors are arranged at a peripheral distance around the cable and respond to the magnetic field generated by a current induced in the conductor. This known device furthermore has two optical arrangements that are offset relative to each other by 90° so that their measurement axes are perpendicular to each other. The position of the cable jacket can be determined with the aid of these optical arrangements.
This known device is provided with a measuring head which can be displaced, for example in horizontal and vertical direction, and for which the position can be adjusted such that the conductor is centered relative to the measurement head.
A method and a device for testing the wall thickness of an insulating layer are furthermore known from Swiss reference CH 667 327 A5. This device comprises on the one hand a measuring device for determining the external diameter and, on the other hand, a measuring device for determining the wall thickness of the insulating material. The determined measuring values are supplied to a computer which then computes the eccentricity of the conductor and the wall thickness. The measuring device for measuring the wall thickness of the cable insulation is an inductive measuring device which operates based on the eddy current principle and determines the distance between the sensor and the conductor surface. A measuring principle of this type is called “passive” within the framework of the present documents, meaning no current is supplied to the cable conductor. The measuring coils in that case are active coils that are arranged symmetrical to the central axis of the device and form a component of a resonating circuit. They measure the eddy current generated by the conductor, from which the distance to the conductor surface is determined.
With this known device, the two aforementioned measuring devices are positioned at a distance to each other in axial direction and thus in the direction of the conductor. As a result, the optical measuring plane and the inductive measuring plane also are at a distance to each other.
Within the framework of the present documents, a measurement or a measuring system is considered active if a current is induced in the conductor, for example a high-frequency alternating current with the aid of an inductor. The magnetic field lines of the field generated in this way extend concentrically around the conductor or the conductor axis and are detected with passive coils.
A different device for determining the position of a conductor relative to the external surface of an extruded coating is known from EP-A-0 612 975. In this reference it is emphasized that it is important for the electrical and mechanical characteristics of an extruded cable to position the conductor along the central cable axis. To determine the eccentricity, this known device uses a combination system, comprising an optical device for determining the cable position in one measuring plane and an inductively operating device for determining a conductor position inside the insulation material or the jacket.
The optical device is provided with two light sources, arranged at an angle of 90° to each other, which emit light perpendicular to the longitudinal cable axis of onto the cable and thus in the direction of the X-axis as well as in the direction of the Y-axis. Respectively one light-measuring device is arranged opposite the light sources, thus making it possible to determine the position of the cable in the measuring plane as well as the external diameter of the cable to be measured.
Also provided are two pairs of induction coils which are arranged on both sides of the cable, wherein one coil pair is arranged in the direction of the X-axis and the other pair in the direction of the Y-axis. If the conductor of the cable to be measured is admitted with an alternating current, a magnetic field is generated which is measured by the induction coils. If the currents measured in the induction coils are equally strong, the conductor is located in the center between the coil pairs and thus is in a central position.
Since the position of the outer cable jacket surface is known from the optical measurement and the position of the conductor is known from the inductive measurement, the centricity of the conductor can be calculated.
With this known device, the measuring planes for the optical measurement and the inductive measurement are arranged axially one behind the other. Thus, if the optical measurement and the inductive measurement occur simultaneously at an optional point in time, the values determined in the process refer to different and axially spaced apart measuring planes and thus different locations or positions of the extruded cable. In addition, grave measurement errors occur if the conductor axis is tilted relative to the central axis of the device or encloses an angle with this central axis.
Additional devices of the type discussed herein are described in references CH-A 542 426, CH-A 683 370 and CH-A 463 124. A new method for measuring the diameter of a harness is explained in reference DE-A 197 57 067.
It is the object of the present invention to provide a measuring system which makes it possible to easily and simultaneously measure the external diameter of a harness, in particular a cable, and the eccentricity of a conductor for this harness/cable, for the same harness location.
This object is solved with the disclosed device.
With the measuring system according to the invention, the harness or the cable to be measured, in particular produced through extrusion, is essentially pulled in the direction of the central axis through the measuring device according to the invention. The system in particular represents a type of measurement yoke, which will be discussed later on.
The cable conductor is provided with an insulating jacket. If the conductor is centered inside this jacket and if the cable to be measured extends or is pulled in the direction of the central axis, as well as is guided and thus pulled centrally through the measuring device or the measurement yoke, then the conductor axis coincides with the central axis of the measuring device according to the invention. With the measuring device according to the invention, however, it is possible to determine reliable and exact values even if the conductor axis, for example, is displaced relative to the central axis—regardless of whether it is centered in the cable or not—or if the conductor axis is tilted relative to the central axis. Further explanations for this can be found below.
An optical measuring device is used to determine the external diameter that is determined in an optical measuring plane. The measuring plane for this optical measuring device is here arranged perpendicular and transverse to the central axis of the measuring device. In other words, the central axis of the measuring device and also the conductor axis form the normal to this optical measuring plane.
Furthermore, the position of the coating (more precisely the outer jacket surface) and thus the position of the cable in the optical measuring plane is determined with the optical measuring device. In other words, it is possible to determine whether the central longitudinal axis of the cable coincides with the central axis of the optical measuring device and thus runs through the central measuring point S or is displaced relative to this point. The longitudinal axis of the cable in this case must be distinguished from the conductor axis of the cable since the latter can be positioned eccentrically inside the jacket and in that case does not coincide with the central axis of the measuring device, even if the longitudinal axis of the cable and the central axis of the measuring device coincide.
The optical measuring device can be a known optional device. Various measuring devices of this type are known and described in the above-listed references. The type of optical measuring device used is therefore not critical. For example, the optical measurement can be realized with a laser scanner or a CCD camera or on a photometric basis.
The optical measuring device advantageously is designed such that the position and diameter of the cable are determined in X-direction and Y-direction, wherein these two directions in particular are perpendicular to each other, are positioned one on top of the other, and enclose a 90° angle.
In the latter case, the optical measuring device usefully consists of two optical measuring systems, which are synchronized through a joint triggering of the measurement (shutter, flash, readout of CCD or the like). Furthermore, the two optical measuring systems are synchronized through a synchronous control of optical scanners and the use of a joint scanner (polygonal mirror) and a ray path that is correspondingly developed with the aid of a mirror. For an optical measurement by means of laser beams, respectively one laser with optical scanner can be used for each measurement axis, respectively for the X-direction and the Y-direction.
It is also possible to realize the optical measurement with more than two measuring systems, for example three measuring systems. In the latter case, the measurement axes and the measurement directions preferably form an angle of 60°, wherein all of these measurement directions and measurement axes are located in a single measuring plane.
However, the device according to the invention preferably has an optical measuring device with two light sources, which are in particular arranged offset at a 90° angle relative to each other and emit light in the optical measuring plane. This light impinges on the harness and is detected on the opposite side of the harness by respectively one sensor that is assigned to the light source.
The device according to the invention is furthermore provided with an inductive measuring coil arrangement for determining the position of the cable conductor in the inductive measuring plane. The measuring plane for this inductive measuring coil arrangement, here also referred to as inductive measuring plane, also extends perpendicular and transverse to the central axis of the measuring device and thus also to the conductor axis.
The device according to the invention is distinguished in that the measuring coils of the measuring coil arrangement are arranged in pairs or are cut in half with respect to the optical measuring plane. As a result, different field intensities are determined on the one hand in front of the optical measuring plane and on the other hand behind the optical measuring plane. The determined field intensities are then correlated, in such a way that the field intensity in the so-called inductive measuring plane is obtained, which coincides with the optical measuring plane by forms a joint, active measuring plane M that simultaneously forms the optical measuring plane.
The expression “in pairs” is intended to indicate the existence of a pair of measuring coils and thus two measuring coils. One of these measuring coils is located in front of the active measuring plane and the other one is located symmetrically thereto on the other side and thus behind the active measuring plane M.
The expression “cut in half” refers to a measuring coil where half of the effective surface of this measuring coil is located on one side of the measuring plane M and determines the field intensity there while the other half is located on the other side of the measuring plane M and determines the field intensity there. The actual inductive measuring plane in that case corresponds to the active measuring plane. The measuring plane so-to-speak cuts in half the effective surface of the measuring coil, thus correlating the two field intensities, measured in front of and behind the measuring plane with the measuring coil embodied in this way, to each other in such a way that a joint measuring plane results, respectively the inductive measuring plane coincides with the optical measuring plane, thus forming the active measuring plane.
With the arrangement in pairs of the measuring coils, the field intensities measured by the individual measuring coils of a pair are correlated in a computation. In other words, the computation determines the field intensity in a type of visual measuring plane. It is not the concrete field intensity that is determined in this virtual plane, which corresponds to the optical measuring plane and represents the joint active measuring plane M. Rather, the field intensity is determined through computation in this virtual measuring plane.
According to a preferred embodiment, all measuring coils in the measuring coil arrangement have the same effective surface and preferably the same form and surface area. The effective surface in this case is understood to mean the surface through which the field lines penetrate in perpendicular direction. If the surface spanned by the coil of a measuring coil is arranged perpendicular to the field lines, then the spanned surface area corresponds to the effective surface. However, if the arrangement is not perpendicular and the field lines penetrate the spanned surface at an angle of less than 90°, then the effective surface is smaller than the spanned surface area. For example, if two measuring coils have the same effective surface, then the voltage induced in those two measuring coils is the same if the field intensity is the same. In the case of a measuring coil pair, one measuring coil of the two measuring coils is used for a measurement in front and the other one for a measurement behind the measuring plane M.
The measuring system according to the invention is furthermore provided with means that correlate the data, determined with the optical measuring device for the cable position, with the data determined with the inductive measuring coil arrangement for the position of the conductor. These means include, for example, a computer unit that is known per se.
The position of the cable in the active measuring plane M and thus also the position of the outer jacket surface for the cable cover is calculated from the data obtained with the aid of the optical measurement, wherein the cable diameter is also determined in the process. In other words, the position of the cross-sectional surface of the cable in the measuring plane is determined optically. As a result of the data obtained during the inductive measurement, the position of the conductor inside the cable is determined in the active measuring plane M. Since the position of the cross-sectional surface in the measuring plane is known, it is possible to use the inductive measurement data in a calculation to determine where the conductor is located in the cross-sectional area. If the conductor for a round cable, for example, is located in the center of the circular cross-sectional area, then the conductor is arranged centrally. If the conductor is not located in the center, then the conductor axis is displaced relative to the centered longitudinal axis of the cable, meaning it is eccentric.
The above statement is also true if the cable and thus its longitudinal axis is displaced to the side or tilted relative to the central axis of the measuring device. This optical measuring device is used to determine the position and the expansion of the cross-sectional area in the measuring plane, which also shows whether or not the longitudinal axis runs through the central measuring point S in the measuring plane, wherein the latter is preferred since the measuring accuracy is highest in that case and the measurement has linearity. For that reason, the optical measuring device and the inductive measuring coil arrangement are designed to be displaceable. If possible, this displacement, the measuring should be realized such that the cable to be measured extends through the central measuring point during the measuring operation.
The measuring system according to the invention furthermore includes all electronic components required for the measurement and processing of the measured data, e.g. amplifiers, converters, etc., wherein such components are known and do not require further explanations.
The optical measurement and the inductive measurement are advantageously carried out at the same time. In other words, both measurements relate to the same location or position of the cable to be measured.
The optical measurement and the inductive measurement preferably take place in real time and the resulting data are also processed in real time.
The inductive measurement realized with the inductive measuring coil arrangement can be either passive or active. However, the inductive measurement preferably takes the form of an active measurement, for which the device according to the invention is provided with a device for inducing a high-frequency alternating current in the conductor of the cable to be measured.
For the inductive measurement, the field lines for the field induced by the current in the conductor run concentrically around this conductor. To determine the intensity of this field, measuring coils can be used for which the winding and the effective surface may be located in a plane that extends perpendicular to the field lines and through which the lines extend at a right angle. It makes sense if two coils are used for the measurement in a plane, which are arranged symmetrical to the central axis Z of the measuring device.
In principle, it is sufficient to carry out the inductive measurement in one plane, wherein the same is true for the optical measurement.
For an inductive measurement in one plane, it is necessary to measure the field intensity on two sides of the central axis Z, meaning in front and behind the measuring plane M. This can be achieved by using two separate measuring coils for each plane for the measuring on one side of the plane M, wherein these coils are arranged symmetrical to the central axis Z. Two different separate measuring coils of this type are present on the other side of the measuring plane M.
This can furthermore be achieved by using measuring coils which are here referred to as differential coils. Differential coils are coils for which the effective surface, which can also be called the effective measurement surface, is divided into two halves with respect to the central axis Z. These two surfaces are preferably located in one plane, so that the one surface measures the field intensity on one side of the central axis Z, while the other surface measures the field intensity on the other, opposite side of central axis Z. The total measurement field is thus cut in half by the central axis Z.
A measurement with three separate measuring coils is possible as well, wherein these measuring coils are preferably arranged in a star-shaped pattern and at angles of 120°. The field intensities measured by the coils are then correlated in such a way that the position of the conductor in the inductive measuring plane results.
The inductive measurement is preferably realized in two planes, here referred to as X-plane and Y-plane, wherein the X-plane and Y-plane enclose an angle that is preferably 90° in this case. The X-plane and the Y-plane are furthermore perpendicular to the measuring plane M or they intersect with this plane at a right angle, thus spanning so-to-speak a three-dimensional space. The central axis Z for the measuring device forms the intersecting line for the X-plane and the Y-plane and extends through the central measuring point S in the active measuring plane M.
Of course, the number of planes in which an inductive measurement is carried out can also be increased, e.g. to three planes that advantageously enclose an angle of 60°. Even if the measuring accuracy is increased by this, an inductive measurement (and also an optical measurement) in two planes and/or directions is normally sufficient.
In principle, an optional number of separate measuring coils can be used for the inductive measurement.
The separate measuring coils for the inductive measurement are preferably distributed evenly in peripheral direction around the central axis Z.
To carry out the optical measurement as well as the inductive measurement in a joint plane, namely the active measuring plane M, separate measuring coils are positioned in a first embodiment in such a way that they are so-to-speak divided in half by the measuring plane of the optical measuring device. This optical measuring plane also represents the inductive measuring plane, so that it forms the joint active measuring plane M.
Since it is difficult for spatial reasons to position the measuring coils in this measuring plane M and simultaneously if possible carry out the optical measurement in two directions that are perpendicular to each other in the measuring plane M, it is advantageous if the X-direction and the Y-direction of the optical measuring device are not located in the X-plane and the Y-plane in which the measuring coils are located. Rather, this X-direction and the Y-direction are offset by an angle, in particular a 45° angle, with respect to the X-plane and the Y-plane.
According to a different embodiment, the measuring coil arrangement for the device according to the invention comprises four measuring coil pairs. Four separate measuring coils of these measuring coil pairs are arranged in the X-plane while four additional, separate measuring coils are arranged in the Y-plane. For this, one measuring coil of a measuring coil pair is positioned in front of the measuring plane M and the other measuring coil of the measuring coil pair is positioned behind the measuring plane M. The measuring coils are arranged symmetrical to the active measuring plane M and preferably also to the measurement axis Z, so that a point symmetry results with respect to the central measuring point S.
The field intensity (or voltage) determined with one measuring coil and the field intensity (or voltage) determined with the second measuring coil of this measuring coil pair are thus added up. The same holds true for the measuring coil pair on the other side of the central axis Z. The resulting difference shows the field intensity computed for the measuring plane M. The effective surfaces of all four measuring coils in this case should be the same.
In another preferred embodiment of the invention, differential coils are used, for which the effective surface is located in the X-plane or the Y-plane. The inductive measurement in that case can be realized in more than two planes, e.g. three or four planes, wherein this requires a corresponding increase in the number of differential coils.
According to one preferred embodiment, the differential coils have a winding that is divided into sections extending on both sides of the central axis Z, as well as parallel thereto, meaning either in the X-plane or the Y-plane. These parallel sections are connected through connecting bends that extend concentric to the central axis Z. Since these connecting bends extend in the direction of the field lines, they are effect-neutral. Thus, the effective surface covers only the surface spanning the area between the two parallel sections of the coil.
The sections extending between two connecting bends must not necessarily extend parallel to the central axis Z. Rather, it is conceivable that these sections extend in a curved shape in the X-plane or the Y-plane, wherein of course the two effective surfaces on both sides of the central axis Z must be identical in size.
The device according to the invention furthermore preferably comprises means for displacing and adjusting either the optical measuring device or the inductive measuring coil arrangement. These means include, for example, a positioning system with positioning drives and a respective control. Also provided are means for measuring the voltage, determining the phase etc. and for processing the obtained data, such as a computer unit. However, these means are all known means and need not be explained further.
The subject matter furthermore includes a method.